Liquid ion exchange recovery of metal values from aqueous solutions is rapidly reaching extensive commercial acceptance. Such processing has been described as being deceptively simple since all that is really happening is the transfer of a metal value from Phase A (aqueous) to Phase B (organic) and thence from Phase B to Phase C (aqueous). However, complexities of liquid ion exchange arise in a number of areas including (1) synthesis and manufacture of the reagent system, (2) evaluation of the system's capabilities, and (3) engineering application leading to large scale metal recovery.
The key to a successful application of liquid ion exchange is the reagent. In this respect, the reagent should meet a number of criteria. In the first instance, the reagent must complex with or react with a metal or group of metals. It is also desirable that the reagent shows preference for a single metal where the aqueous starting solutions contain a number of metal values. The reagent should also desirably complex or react to a high degree of completion with the metal under the extraction conditions. Additionally, the reagent, as well as the resulting metal complex, must exhibit satisfactory solubility in practical solvents. Further, the reagent-metal reaction must be reversible so that the metal can be stripped. For economic reasons, the reagent must be acceptably stable so that it can be recycled repeatedly. Also, it should be essentially water insoluble to prevent significant loss into the aqueous phase. Furthermore, the reagent should not cause or stabilize emulsions. And, of course, the cost of the reagent should be such that the liquid ion exchange process can be operated at a profit.
A few compounds have found significant commercial acceptance. U.S. Pat. No. 4,563,256 describes a solvent extraction process for the recovery of zinc values from ammoniacal solutions, which may also contain copper values, using or employing various oxime extractants.
U.S. Pat. No. 2,727,818 describes a method of leaching copper sulfide materials with ammoniacal leach solutions. No solvent extraction is discussed.
U.S. Pat. Nos. 4,065,502 and 4,175,012 describes beta-diketones which may be employed as metal extractants in a liquid-liquid ion exchange process for recovery of metals, such as nickel or copper, from aqueous solutions containing the metal values, including aqueous ammoniacal solutions.
U.S. Pat. No. 4,350,661 describes the extraction of copper from ammoniacal aqueous solutions by a process of extraction first with a beta-diketone followed by a second extraction with an oxime. Alternatively, there is described the use of a mixture of diketone and oxime wherein the extractant reagent comprises about 5-30 percent by volume of the strong reagent (oxime) and 10-60 percent by volume of the weak reagent (beta diketone).
In commonly assigned, co-pending application, U.S. Ser. No. 08/780,759, the entire disclosure of which is hereby incorporated by reference, there is described a sterically-hindered beta-diketone which, due to the steric hindrance around the beta-diketone functionality results in more stability to use conditions, minimizing, if not eliminating, ketimine formation.
While these sterically-hindered beta-diketones appear to be highly effective metal extractants, their production in economically acceptable yields, in the absence of unwanted by-product formation, remains a problem. The utilization of known production techniques results in either low yields and/or the formation of unwanted by-products such as dypnone, which are very difficult to separate from the sterically-hindered beta-diketone product.